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A Guide to Collaborative Robot Safety

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The ability of collaborative robots to share tasks with humans and flexibly adapt to new requirements can provide high returns on investment in a wide variety of industrial applications. Manufacturers employ these robots to reap the benefits of integrated safety features that allow them to work with or close by humans and boost productivity for a wide variety of repetitive tasks.

Despite the numerous safety features that include lightweight frames, collision detection technology, and minimized pinch points, appropriate safety measures must still be considered for the overall application — including the gripper, end effector, and other equipment located near the collaborative workspace. Safe implementation based on comprehensive risk assessments is crucial for ensuring the success of a collaborative robotic application.

This article discusses industry standards, project stages, and solutions for getting the greatest value from collaborative robots (commonly shortened to “cobots”). It also defines and discusses safety requirements for the robots themselves as well as the collaborative workspace and typical collaborative operations.

What are Cobots, and What Safety Standards Apply?

Collaborative robots are designed to work with human operators thanks to technologies like force feedback, low-inertia servomotors, elastic actuators, and collision detection technology that limit their power and force capabilities to levels suitable for contact. More compact than conventional robots, cobots generally have lightweight frames with soft, rounded edges and minimized pinch points (Figure 1).

Force and speed monitoring are the defining abilities of collaborative robots. When they are equipped with safety devices that detect when a person has entered the collaborative workspace, they are often allowed to operate at higher speeds. This helps them maximize throughput when people are not present within the hazard zone.

The safety standard ISO 10218 and technical specification RIA TS 15066 define the safety functions and performance of the collaborative robot. Under TS 15066, the force and speed monitoring of the cobot is set based on application data, human contact area, and workspace hazards. Human contact is defined in two types: transient and quasi-static. The former refers to contact that is non-clamping, whereas the latter involves situations that can cause a body part to be clamped.

Application data, possible human contact, and workspace hazards all factor into the calculated safety settings based on TS 15066. This may be a challenging task for manufacturers who are not familiar with safety standards, in which case they can hire a safety assessment provider to make the calculations and offer suggestions for improving the safety of the overall collaborative application.

Hand-Guided Teaching Safety Standards

ISO 10218 and ISO/TS 15066 provide standards and guidance for collaborative robot teaching functionality. Many cobots, such as Omron’s TM Series robot, employ intuitive hand-guiding mechanisms for teaching new tasks without the need to explicitly program the movements of the robotic arm. Hand-guiding mode monitors force and speed to ensure that the teaching process complies with safety standards.

Enabling hand guiding. Before an operator enters the robot’s workspace for teaching, the robot must be stopped even if its force and speed-limiting functionality is activated. Otherwise, a protective stop must be executed upon detection of the operator by a safety device like an area scanner.

Unlike with high-speed robots, the operator can activate the teaching mode using a simple trigger, button, or mode selection as long as safety force and speed monitoring are active. Otherwise, a three-position safety enable is required. Safety standards require the teaching mode transition to be deliberate, not lead to unexpected motion, and avoid creating additional hazards.

Figure 2. In a collaborative application, risk assessments must take into account any surrounding equipment in addition to the robot itself.

Ensuring safe teaching. Since the operator is responsible for the robot’s motion, he or she must be aware of surrounding equipment and safety concerns at all times (Figure 2). It is possible to enforce limits in motion, such as space and soft axis limits, to help keep the operator safe.

Enabling safe operation. The operator must first vacate the safeguarded space. This can be detected by safety sensors or additional operator verification. To re-enable the robot for operation, intentional mode selection must be provided.

What is a Collaborative Workspace?

Cobots perform automated tasks around other equipment that could potentially cause harm. The area in which a collaborative robot operates, including any tooling or additional equipment, is known as the collaborative workspace. As defined by ISO 10218/ANSI RIA 15.06, this is the space within the safeguarded area where the robot and human can perform tasks simultaneously during production operations. Similarly, TS 15066 defines it as the area within the operating space where the robot system can perform tasks concurrently with a human operator during production.

It is important to list and map out all additional equipment in the complete collaborative automation project. Manufacturers should be sure to evaluate each device for potential hazards and safety sensors to use to prevent human and equipment damage. In addition, the collaborative workspace must be clearly marked.

The following are examples of noncollaborative safety-rated equipment that can be part of the workspace requiring safety devices:

Material handling

Tooling

Grippers/actuators

Machines

Safety devices are generally quite easy to integrate into a collaborative robotic application. Following are a few solutions for safeguarding the collaborative workspace.

Open area safety guarding solutions. Safety area scanners and mats are the most popular safeguarding for cobots. They are also some of the simplest items to integrate into applications with low hazards and few additional pieces of equipment.

Gated/limited area safety guarding solutions. Safety light curtains and safety switches are used for applications with hazards or high-speed operation enablement for increased productivity.

Active hazards safety guarding solutions. When a hazard is present or operation could cause a hazard, operators can enable the “deadman” switch — a switch that automatically goes back to the “off” position if the user fails to exert pressure.

Maximizing safety in collaborative operations. It is essential for manufacturers to validate their cobot applications for safety across all operations. Every application is unique, but there are some guidelines manufacturers can follow when evaluating the safety of a robot while performing a given task in collaboration with a human operator. Drive and power hazards may still exist even if the robot is not moving.

Safe robot enable. Whether starting up the robot or recovering from an emergency stop, there must be an intentional act to enable the robot that ensures operators are safe and no hazards are present; for example, when an e-stop is activated by an operator, the robot should not perform an automatic re-enable. Instead, it should require input from a second operator verification action.

Safe hand guiding. During design and safety setup, manufacturers must ensure that hand-guiding can only occur after (1) the robot has stopped, (2) intentional mode selection has occurred, and (3) speed and force monitoring are active. If hand-guiding activation occurs without a stop command or safety input, this should initiate a safety stop and fault.

Safe operation. Enabling the automatic or run operation of the cobot must be an international mode selection by the operator that requires all safety devices and conditions to be validated for operation. Operators must be protected from hazards on the end-of-arm tooling before enabling operation.

Safety validation. It is important for manufacturers to have a safety assessment service group review all the surrounding areas and equipment and to have a safety remediation service performed if necessary. Safety service groups will perform an on-site inspection to assess the safety of equipment, confirm certifications, verify safety parameter settings, and document that safety validation has been completed.

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